# The CN-CH positive correlation in the globular cluster NGC 5286

## TL;DR

This study reveals a positive correlation between CN and CH indices in NGC 5286, indicating multiple stellar populations with heavy element variations and supernovae enrichment, which is unusual among globular clusters.

## Contribution

It demonstrates the presence of a CN-CH positive correlation in NGC 5286, linking it to heavy element abundance variations and multiple stellar populations.

## Key findings

- Stars are divided into three subpopulations by CN index.
- CN-strong stars are enhanced in calcium and CH indices.
- The positive CN-CH correlation is unique among globular clusters with heavy element variations.

## Abstract

We performed low-resolution spectroscopy for the red giant stars in the Galactic globular cluster (GC) NGC 5286, which is known to show intrinsic heavy element abundance variations. We found that the observed stars in this GC are clearly divided into three subpopulations by CN index (CN-weak, CN-intermediate, and CN-strong). The CN-strong stars are also enhanced in the calcium HK' (7.4{\sigma}) and CH (5.1{\sigma}) indices, while the CN-intermediate stars show no significant difference in the strength of HK' index with CN-weak stars. From the comparison with high-resolution spectroscopic data, we found that the CN- and HK'-strong stars are also enhanced in the abundances of Fe and s-process elements. It appears, therefore, that these stars are later generation stars affected by some supernovae enrichment in addition to the asymptotic giant branch ejecta. In addition, unlike normal GCs, sample stars in NGC 5286 show the CN-CH positive correlation, strengthening our previous suggestion that this positive correlation is only discovered in GCs with heavy element abundance variations such as M22 and NGC 6273.